1. Field of the Invention
The present invention relates to an image display device which drives the current of a light emitting device arranged for every pixel for display. More specifically, the invention relates to a so-called active matrix image display device which controls the amount of current carried through a light emitting device such as an organic electroluminescent device with an insulating gate field effect transistor arranged in individual pixel circuits. In addition, the invention relates to an electronic appliance in which a display device like this is assembled therein.
2. Description of the Related Art
In image display devices such as a liquid crystal display, a large number of liquid crystal pixels are arranged in a matrix, the transmission intensity or the reflection intensity of incident lights is controlled for every pixel depending on image information to be displayed, and then an image is displayed. This is the same in an organic electroluminescent display in which an organic electroluminescent device is used for pixels, but the organic electroluminescent device is a self light emitting device different from the liquid crystal pixel. On this account, the organic electroluminescent display has higher image visibility than that of the liquid crystal display, and a back light is unnecessary, having advantages such as high response speed. In addition, the brightness level (gray scale) of individual light emitting devices can be controlled by the value of current carried therethrough. The organic electroluminescent display is greatly different from a voltage control display such as the liquid crystal display in that the organic electroluminescent display is a so-called current control display.
As similar to the liquid crystal display, the organic electroluminescent display has the drive modes as the simple matrix mode and the active matrix mode. The former has a simple structure, but has a problem that it is difficult to implement a display in large size and high definition. Thus, nowadays, the active matrix mode displays are being actively developed. In this mode, current carried through a light emitting device inside individual pixel circuits is controlled by an active device (generally a thin film transistor: TFT) disposed inside the pixel circuit, and this mode is described in JP-A-2003-255856, JP-A-2003-271095, JP-A-2004-133240, JP-A-2004-029791 and JP-A-2004-093682.